Boosters for breakers containing iron compounds

ABSTRACT

Methods for fracturing a subterranean formation penetrated by a well bore are provided, the method comprising the step of injecting a well treatment fluid into the well bore at a pressure and flow rate sufficient to fracture the subterranean formation, wherein the well treatment fluid comprises one or more iron-containing compounds and one or more booster compounds. The methods can be used to reduce viscosity and to facilitate the decomposition of acrylamide-containing polymers.

FIELD OF THE ART

The present disclosure relates to boosters for breakers containing ironcompounds and their methods of use in fracturing applications.

BACKGROUND

Fluids exhibit a measurable property known as viscosity, a term whichmay be broadly defined as the internal friction or molecular attractionof a given material which manifests itself in resistance to flow. It ismeasured in liquids by standard test procedures and is usually expressedin poise or centipoise (cP) at a specified temperature, although in oiltechnology it is sometimes expressed in seconds required for a givenvolume to flow through a specified orifice at a definite temperature.The viscosity of a fluid is an indication of a number of behaviorpatterns of the liquid at a given temperature including pumpingcharacteristics, rate of flow, wetting properties, and a tendency orcapacity to suspend an insoluble particulate material.

There are a number of industrial operations wherein it is desirable toemploy viscous aqueous solutions. For example, viscous aqueous solutionsare employed to fracture subterranean formations penetrated by aborehole for increasing the production of petroleum fluids, namely crudeoil and natural gas. Viscous aqueous solutions are also employed in thesecondary recovery of oil from oil bearing subterranean formations byfluid drive processes.

It is common practice to treat subterranean formations to increase thepermeability or conductivity of such formations by procedures that areidentified generally as fracturing processes. For example, it is aconventional practice to hydraulically fracture a well in order toproduce one or more cracks or “fractures” in the surrounding formationby mechanical breakdown of the formation. Fracturing may be carried outin wells that are completed in subterranean formations for virtually anypurpose. The usual candidates for fracturing, or other stimulationprocedures, are production wells completed in oil and/or gas containingformations. However, disposal wells and injection wells used insecondary or tertiary recovery operations, for example, for theinjection of water or gas, may also be fractured in order to facilitatethe injection of fluids into such subterranean formations.

Hydraulic fracturing is accomplished by injecting a well treatment fluidinto the well and applying sufficient pressure on the well treatmentfluid to cause the formation to break down with the attendant productionof one or more fractures. Usually a gel, an emulsion or a foam having aproppant such as sand or other particulate material suspended therein isintroduced into the fractures. The proppant is deposited in thefractures and functions to hold the fractures open after the pressure isreleased and the well treatment fluid flows back to the surface. Thewell treatment fluid must have a sufficiently high viscosity to retainthe proppant in suspension or at least to reduce the tendency of theproppant to settle out as it flows along the created fracture.Viscosifiers, such as a polysaccharide or a polyacrylamide, are oftenused to gel the well treatment fluid to provide the high viscosityneeded to retain the proppant in suspension.

After the high viscosity well treatment fluid has been pumped into theformation and fracturing of the formation has occurred, it is desirableto remove the fluid from the formation to allow hydrocarbon productionthrough the new fractures. Generally, the removal of the highly viscouswell treatment fluid is realized by “breaking” the gel, i.e. convertingthe well treatment fluid into a low viscosity fluid. Breaking the gelledwell treatment fluid has commonly been accomplished by adding a“breaker,” that is, a viscosity-reducing agent, to the well treatmentfluid prior to pumping into the subterranean formation.

Acrylamide-containing polymers are often added to well treatment fluidsin oilfield applications to reduce friction or to modify rheologicalproperties of the fluid. Such polymers may persist in the fluid orformation for an extended period of time. The polymer residue may plugsome of the permeability of the rock, hinder recovery of the water usedin the well treatment fluid, or hinder a source of nitrogen that cansupport the growth of bacteria in the well. In order to facilitateremoval of these polymers after the task has been completed, treatmentsinvolving oxidizer-based breakers, for example persulfate salts, may beapplied. Breakers can be used in this manner to generate smallerpolymeric fragments with more benign environmental profile.

SUMMARY

Disclosed herein is a method for fracturing a subterranean formationpenetrated by a well bore, the method comprising the step of injecting awell treatment fluid into the well bore at a pressure and flow ratesufficient to fracture the subterranean formation, wherein the welltreatment fluid comprises water, at least one acrylamide-containingpolymer, one or more iron-containing compounds and one or more boostercompounds. A method for fracturing a subterranean formation penetratedby a well bore is also provided, the method comprising the steps of (i)injecting a first well treatment fluid comprising at least oneacrylamide-containing polymer into the well bore at a pressure and flowrate sufficient to fracture the subterranean formation; and (ii)injecting a second well treatment fluid comprising one or moreiron-containing compounds and one or more booster compounds into thewell bore. Further, a method for fracturing a subterranean formationpenetrated by a well bore is also provided, the method comprising thesteps of (i) injecting a first well treatment fluid comprising at leastone acrylamide-containing polymer into the well bore at a pressure andflow rate sufficient to fracture the subterranean formation; (ii)injecting a second well treatment fluid comprising one or moreiron-containing compounds; and (iii) injecting a third well treatmentfluid comprising one or more booster compounds into the well bore.

A well treatment fluid comprising water, one or more iron-containingcompounds, one or more booster compounds, and at least oneacrylamide-containing polymer, is also disclosed herein.

Methods for reducing the viscosity of a well treatment fluid are alsoprovided, each method comprising adding one or more iron-containingcompounds and one or more booster compounds to the well treatment fluid,wherein the well treatment fluid comprises water and at least oneacrylamide-containing polymer

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graph of the viscosity (cP) after breaking with exemplaryiron-containing compounds or commercially available breakers, alone orin combination with exemplary booster compounds.

DETAILED DESCRIPTION

Disclosed herein are well treatment fluids and methods of use whichinclude one or more iron-containing compounds and one or more boostercompounds. The exemplary combinations of the one or more iron-containingcompounds and one or more booster compounds may be used to reduce theviscosity of a well treatment fluid as used, for example in methods offracturing subterranean formations. The exemplary combinations can beused in aqueous fluids, including well treatment fluids, to reduce themolecular weight of an acrylamide-based polymer contained in the fluid.The exemplary combinations and methods can be used advantageously tofacilitate the breakdown of acrylamide-based polymers into smallerfragments. The methods may be readily incorporated into currentprocessing facilities and may provide economic and environmentalbenefits.

Breakers and Breaker Compositions

As used herein, the term “breaker” refers any compound or mixture ofcompounds which reduces the viscosity of the well treatment fluid. Inexemplary embodiments, the breaker is one or more iron-containingcompounds, for example a ferrous compound, ferrous salt, ferriccompound, ferric salt, and mixtures thereof. In exemplary embodiments,the ferrous salt is, for example, a ferrous salt having an organicanion, a ferrous salt having an inorganic anions, or a mixture thereof.In exemplary embodiments, the breaker or ferrous salt is ferrouschloride, ferrous bromide, ferrous fluoride, ferrous sulfate, ammoniumiron sulfate and combinations thereof. In exemplary embodiments, theferrous salt breaker comprises ferrous sulfate.

In exemplary embodiments, the ferric salt is, for example, a ferric salthaving an organic anion, a ferric salt having an inorganic anions, or amixture thereof. In exemplary embodiments, the breaker or ferric salt isferric citrate, ferric chloride, ferric bromide, ferric fluoride, ferricsulfate, and combinations thereof. In exemplary embodiments, the ferricsalt breaker comprises ferric citrate.

In exemplary embodiments, the breaker may be used or combined with otherbreakers, for example ammonium sulfate, ammonium persulfate, enzymes,copper compounds, ethylene glycol, glycol ethers and combinationsthereof. In exemplary embodiments, the breaker comprises ferrous citratein combination with ammonium persulfate. In exemplary embodiments, thebreaker comprises ferrous sulfate in combination with ammoniumpersulfate.

In exemplary embodiments, the breaker may be used to facilitatedecomposition of an acrylamide-containing polymer or gel composition. Inexemplary embodiments, the breaker may be used to reduce the viscosityof an acrylamide-containing polymer or gel composition. In exemplaryembodiments, the breaker may be used to facilitate decomposition of agel composition or acrylamide-containing polymer into oligomericfragments.

In exemplary embodiments, a breaker composition may consist essentiallyof one or more iron-containing compounds or may comprise the one or moreiron-containing compounds, solvents, diluents, other breakers, and/orother suitable additives.

In exemplary embodiments, the breaker composition may comprise, or beused in combination with, one or more compounds or agents which mayenhance or boost the performance of the breaker composition, e.g.booster compounds. Exemplary booster compounds may be used to enhancethe rate of breaking compared to the rate of the breaker compound orcomposition in the absence of booster compounds. For example, boostercompounds include, but are not limited to, urea;ethylenediaminetetraacetic acid (EDTA); salts of EDTA, e.g. sodium saltsof EDTA; or other chelating agents such as citric acid,aminotricarboxylic acid and its salts, polyphosphonated and polyphosphate compounds, boric acid and its salts, alkali metal salts ofcarbonates, diethylenetriaminepentaacetic acid (DTPA), humic acids, andlignosulfates. Polyphosphonates include, for example,ethylenediaminetetra(methylenephosphonic acid); 1-hydroxyethylidene-1,1-diphosphonic acid and aminotri(methylene phosphonic acid) and theirsalts. Examples of polyphosphates include adducts made from the reactionof polyhedric solvents such as glycerin and ethylene glycol with P₂O₅ toform polyphosphated mixtures. In a particular embodiment, the boostercompound is urea, EDTA or a salt of EDTA. In another particularembodiment, the booster compound is a sodium salt of EDTA.

Acrylamide-Containing Polymers

In exemplary embodiments, the breaker may be used to facilitatedecomposition of an acrylamide-containing polymer or gel composition,for example decomposition of an acrylamide-containing polymer intooligomeric fragments.

As used herein, the terms “polymer,” “polymers,” “polymeric,” andsimilar terms are used in their ordinary sense as understood by oneskilled in the art, and thus may be used herein to refer to or describea large molecule (or group of such molecules) that contains recurringunits. Polymers may be formed in various ways, including by polymerizingmonomers and/or by chemically modifying one or more recurring units of aprecursor polymer. A polymer may be a “homopolymer” comprisingsubstantially identical recurring units formed by, e.g., polymerizing aparticular monomer. A polymer may also be a “copolymer” comprising twoor more different recurring units formed by, e.g., copolymerizing two ormore different monomers, and/or by chemically modifying one or morerecurring units of a precursor polymer. The term “terpolymer” may beused herein to refer to polymers containing three or more differentrecurring units. A polymer may also be linear, branched or crosslinked.

As used herein, the term “acrylamide-containing polymer” includesacrylamide homopolymers, copolymers, and terpolymers; polyacrylamide;polyacrylamide derivatives; partially hydrolyzed polyacrylamide;partially hydrolyzed polyacrylamide derivatives; methacrylamidehomopolymers, copolymers, and terpolymers; diacetone acrylamidepolymers; N-methylolacrylamide polymers; friction-reducing acrylamidepolymers; and combinations thereof. In exemplary embodiments, theacrylamide-containing polymer may contain any suitable monomers, forexample vinyl acetate, N-vinylformamide, N-vinylacetamide,N-vinylcaprolactam, N-vinylimidazole, N-vinylpyridine,2-acrylamido-2-methylpropanesulfonic acid (AMPS), N-vinylpyrolidone,acrylamidopropyltrimonium chloride, or combinations thereof.

In exemplary embodiments, the acrylamide-containing polymer is acopolymer. In exemplary embodiments, the copolymer contains about 1 toabout 99, about 5 to about 95, about 10 to about 90, about 20 to about80, about 30 to about 70, about 40 to about 60 weight percent ofacrylamide, methyacrylamide or acrylamide derivatives.

In exemplary embodiments, the acrylamide-containing polymer is afriction reducer or friction-reducing polymer. As used herein, the term“friction reducer” or “friction-reducing polymer” is a compound orcomposition of compounds which reduces the friction between the welltreatment fluid and pipe and/or allows pumps to pump at a higher ratewithout having greater pressure on the surface. In exemplaryembodiments, the friction reducer comprises an acrylamide-containingpolymer, for example polyacrylamide, polyacrylamide derivatives, andcombinations thereof.

In exemplary embodiments, the friction reducer further comprises othersuitable polymers selected from the group consisting of polyacrylicacids, polyacrylic salts, acrylate copolymers containing acrylamide,acrylonitrile and combinations thereof. Other suitable polymers will beapparent to those of skill in the art and are to be considered withinthe scope of the present invention.

In exemplary embodiments, the acrylamide-containing polymer is aviscosifier. As used herein, the term “viscosifier” refers to a compoundor composition of compounds which increases the viscosity of the welltreatment fluid. In exemplary embodiments, the viscosifier comprises athickening polymer such as a hydratable polymer such as, for example,one or more polymer capable of forming linear or crosslinked gels.

In exemplary embodiments, the at least one acrylamide-containing polymeris in the form of a polymer composition or gel composition. In exemplaryembodiments, the at least one acrylamide-containing polymer may becrosslinked or in the presence of crosslinking agents in a polymercomposition or gel composition.

Well Treatment Fluids

As used herein, the terms “well treatment fluid”, “pressurized fluid” or“fracturing fluid” refer to a fluid composition that useful in oil fieldapplications including, for example, low-volume hydraulic fracturing,high-volume hydraulic fracturing, slick water fracturing and wellstimulation; for oil, gas or geothermal energy wells, as well as cleanuprelated thereto. In exemplary embodiments, the well treatment fluid canbe an aqueous fluid, gel, foam or slick water-based. In exemplaryembodiments, the well treatment fluid is of sufficient viscosity tofacilitate fracturing of a formation.

In exemplary embodiments, a well treatment fluid comprises one or moreiron-containing compounds and one or more booster compounds. Inexemplary embodiments, the one or more booster compounds are selectedfrom the group consisting of: urea; EDTA; salts of EDTA; citric acid;aminotricarboxylic acid and its salts; polyphosphonated and polyphosphate compounds; boric acid and its salts; alkali metal salts ofcarbonates, diethylenetriaminepentaacetic acid (DTPA), humic acids, andlignosulfates. In exemplary embodiments, the well treatment fluidfurther comprises water and at least one acrylamide-containing polymer.

In exemplary embodiments, the well treatment fluid is used in ahydraulic fracturing application before, with or after other welltreatment fluids. Other well treatment fluids include, for example, awell treatment fluid that comprises water and at least oneacrylamide-containing polymer. In exemplary embodiments, the welltreatment fluid may further comprise other viscosifiers, other frictionreducers, proppants, acids, sodium chloride, emulsifiers, sodium andpotassium carbonates, biocides, anti-scaling compounds, corrosionpreventing compounds, or other suitable additives.

In exemplary embodiments, the well treatment fluid comprises water,wherein the water is selected from fresh water, brine, aqueous-basedfoams, water-alcohol mixtures, and combinations thereof.

In exemplary embodiments, the at least one acrylamide-containing polymeris in an amount of about 0.001% to about 5%, 0.001% to about 1%, 0.001%to about 0.5%, about 0.001% to about 0.4%, or about 0.001% to about 0.2of the well treatment fluid volume.

In exemplary embodiments, the amount of the one or more iron-containingcompounds in the well treatment fluid is about 0.001% to about 0.2,0.001% to about 0.1%, about 0.001% to about 0.05%, or about 0.075% toabout 0.02% of the well treatment fluid volume.

In exemplary embodiments, the amount of the one or more boostercompounds compounds in the well treatment fluid is about 0.001% to about0.2%, 0.001% to about 0.1%, or about 0.001% to about 0.05 of the welltreatment fluid volume.

In exemplary embodiments, the one or more iron-containing compounds andthe one or more booster compounds in the well treatment fluid arepresent in substantially equivalent amounts by mole.

In exemplary embodiments, the acrylamide-containing polymer is in theform of dry powder or carried (suspended) in liquid such as petroleumdistillate or mineral oil. In exemplary embodiments, theacrylamide-containing polymer may be added in a breaker-free stage or abreaker-laden stage. In exemplary embodiments, when present in the samestage as the breaker, the breaker exhibits some affinity towards thefriction reducer. In exemplary embodiments, the acrylamide-containingpolymer may be added in a viscosifier-free stage or a viscosifier-ladenstage.

In addition to friction reducers, viscosifiers, breakers and proppants,several other additives used in the oil industry and known in the artmay be added to a well treatment fluid. In exemplary embodiments, thewell treatment fluid may further comprise acids, hydrochloric acid,acetic acid, sodium chloride, ethylene glycol, scale reducers, sodiumcarbonate, potassium carbonate, biocides, crosslinking agents, corrosioninhibitors, citric acid, non-emulsifiers, emulsifiers, iron controlagents, delay additives, silt suspenders, flowback additives,isopropanol, methanol, and combinations thereof.

In exemplary embodiments, the well treatment fluid comprises one or moreviscosifiers. In exemplary embodiments, the well treatment fluidcomprises one or more viscosifiers that is an acrylamide-containingpolymer. In exemplary embodiments, the well treatment fluid comprisesone or more viscosifiers that is a hydratable polymer, for examplegalactomannan gums, guars, derivatized guars, cellulose and cellulosederivatives, starch, starch derivatives, xanthan, derivatized xanthanand mixtures thereof. In exemplary embodiments, the viscosifiercomprises a hydratable polymer selected form the group consisting ofguar gum, guar gum derivative, locust bean gum, welan gum, karaya gum,xanthan gum, scleroglucan, diutan, cellulose, cellulose derivatives andcombinations thereof. In exemplary embodiments, the viscosifiercomprises a hydratable polymer selected form the group consisting ofhydroxypropyl guar (HPG), carboxymethyl hydroxypropyl guar (CMHPG),hydroxyethyl cellulose (HEC), carboxymethyl hydroxyethyl cellulose(CMHEC), carboxymethyl cellulose (CMC), dialkyl carboxymethyl cellulose,and combinations thereof. In exemplary embodiments, the viscosifier isselected form the group consisting of phosphomannans, scerolglucans,dextrans and combinations thereof.

In exemplary embodiments, the well treatment fluid comprises acrosslinking agent. In exemplary embodiments, any crosslinking agentsuitable for crosslinking the hydratable polymer may be employed. Inexemplary embodiments, suitable crosslinking agents can be anyconventionally used crosslinking agents which are known to those skilledin the art. In exemplary embodiments, suitable crosslinking agentsinclude borate crosslinkers. In exemplary embodiments, suitablecrosslinking agents include metal ions such as aluminum, antimony,zirconium and titanium-containing compounds, including organotitanates.

In exemplary embodiments, the viscosifier is a guar or derivatized guar.In exemplary embodiments, suitable crosslinkers for guar based polymersinclude borate ion donating materials. In exemplary embodiments,borate-based crosslinkers include, but are not limited to,organo-borates, mono-borates, poly-borates, mineral borates, andcombinations thereof.

In exemplary embodiments, the viscosifier can be in the form of drypowder, carried (suspended) in liquid or dissolved in a liquid. Inexemplary embodiments, the viscosifier may be added in a breaker-freestage or a breaker-laden stage. In exemplary embodiments, when presentin the same stage as the breaker, the breaker exhibits some affinitytowards the viscosifier. In exemplary embodiments, the viscosifier maybe added in a proppant-free stage or a proppant-laden stage. Inexemplary embodiments, the viscosifier may be added in a frictionreducer-free stage or a friction reducer-laden stage.

Methods

In exemplary embodiments, methods are provided for fracturing asubterranean formation penetrated by a well bore, comprising the step ofinjecting a well treatment fluid into the well bore at a pressure andflow rate sufficient to fracture the subterranean formation, wherein thewell treatment fluid comprises water, at least one acrylamide-containingpolymer, a breaker comprising one or more iron-containing compounds andone or more booster compounds. In exemplary embodiments, the welltreatment fluid is a hydraulic fracturing fluid.

In exemplary embodiments, methods are provided for fracturing asubterranean formation penetrated by a well bore, comprising the stepsof (i) injecting a first well treatment fluid comprising at least oneacrylamide-containing polymer into the well bore at a pressure and flowrate sufficient to fracture the subterranean formation; and (ii)injecting a second well treatment fluid comprising one or moreiron-containing compounds and one or more booster compounds into thewell bore. In exemplary embodiments, the first well treatment fluid isinjected into the well bore before the second well treatment fluid. Inexemplary embodiments, the first well treatment fluid is injected intothe well bore substantially at the same time as the second welltreatment fluid. In exemplary embodiments, the first well treatmentfluid is injected into the well bore after the second well treatmentfluid.

In exemplary embodiments, methods are provided for fracturing asubterranean formation penetrated by a well bore, comprising the stepsof (i) injecting a first well treatment fluid comprising at least oneacrylamide-containing polymer into the well bore at a pressure and flowrate sufficient to fracture the subterranean formation; (ii) injecting asecond well treatment fluid comprising one or more iron-containingcompounds; and (iii) injecting a third well treatment fluid comprisingone or more booster compounds into the well bore. In exemplaryembodiments, the first well treatment fluid is injected into the wellbore before the second or third well treatment fluids. In exemplaryembodiments, the first well treatment fluid is injected into the wellbore substantially at the same time as the second and third welltreatment fluids. In exemplary embodiments, the first well treatmentfluid is injected into the well bore after the second and third welltreatment fluids. In exemplary embodiments, the second well treatmentfluid is injected into the well bore substantially at the same time asthe third well treatment fluids. In exemplary embodiments, the firstwell treatment fluid comprising at least one acrylamide-containingpolymer is injected into the well bore before the second well treatmentfluid comprising one or more iron-containing compounds is injected intothe well bore. In exemplary embodiments, the second well treatment fluidcomprising one or more iron-containing compounds is injected into thewell bore before the third well treatment fluid comprising one or morebooster compounds is injected into the well bore. In exemplaryembodiments, the injection of a composition or well treatment fluid asdescribed herein immediately follows the injection of anothercomposition or well treatment fluid, e.g. without delay. In exemplaryembodiments, the injection of a composition or well treatment fluid asdescribed herein follows the injection of another composition or welltreatment fluid within about 5 minutes, about 4, minutes, about 3minutes, about 2 minutes or about 1 minute.

In exemplary embodiments, the first well treatment fluid furthercomprises a proppant. In exemplary embodiments, the second welltreatment fluid further comprises a proppant. In exemplary embodiments,the third well treatment fluid further comprises a proppant.

In exemplary embodiments, the at least one acrylamide-containing polymeris injected into the well bore before the injection of the one or moreiron-containing compound and one or more booster compounds to the welltreatment. In exemplary embodiments, methods are provided for reducingthe viscosity of a well treatment fluid comprising adding one or moreiron-containing compound and one or more booster compounds to the welltreatment fluid, wherein the well treatment fluid comprises water and atleast one acrylamide-containing polymer.

In exemplary embodiments, methods for enhancing the biodegradation of awell treatment fluid are provided, comprising adding one or moreiron-containing compounds and one or more booster compounds to the welltreatment fluid, wherein the well treatment fluid comprises water and atleast one acrylamide-containing polymer.

In exemplary embodiments, the one or more iron-containing compounds andone or more booster compounds reduces the viscosity of the welltreatment fluid over a period of time. In exemplary embodiments, the oneor more iron-containing compounds and one or more booster compoundsreduces the molecular weight of at least one acrylamide-containingpolymer. In exemplary embodiments, the one or more iron-containingcompounds and one or more booster compounds generates fragments of theat least one acrylamide-containing polymer, for example biodegradable oroligomeric fragments. In exemplary embodiments, the addition of the oneor more iron-containing compounds and one or more booster compoundsresults in decreasing the viscosity of the well treatment fluid.

In exemplary embodiments, the one or more iron-containing compounds canbe in the form of dry powder, carried (suspended) in liquid or dissolvedin a liquid. In exemplary embodiments, the one or more booster compoundscan be in the form of dry powder, carried (suspended) in liquid ordissolved in a liquid.

In exemplary embodiments, the method further comprises injecting one ormore additional breakers, for example ammonium sulfate, ammoniumpersulfate, enzymes, copper compounds, ethylene glycol, glycol ethersand combinations thereof.

In exemplary embodiments, the one or more iron-containing compounds maybe added in a viscosifier-free stage or a viscosifier-laden stage. Inexemplary embodiments, when present in the same stage as theviscosifier, the one or more iron-containing compounds exhibits someaffinity towards the viscosifier. In exemplary embodiments, the one ormore iron-containing compounds may be added in a proppant-free stage ora proppant-laden stage. In exemplary embodiments, the one or moreiron-containing compounds may be added in a friction reducer-free stageor a friction reducer-laden stage. In exemplary embodiments, whenpresent in the same stage as the friction reducer, the one or moreiron-containing compounds exhibits some affinity towards the frictionreducer.

In exemplary embodiments, the one or more booster compounds may be addedin a viscosifier-free stage or a viscosifier-laden stage. In exemplaryembodiments, when present in the same stage as the viscosifier, the oneor more booster compounds exhibits some affinity towards theviscosifier. In exemplary embodiments, the one or more booster compoundsmay be added in a proppant-free stage or a proppant-laden stage. Inexemplary embodiments, the one or more booster compounds may be added ina friction reducer-free stage or a friction reducer-laden stage. Inexemplary embodiments, when present in the same stage as the frictionreducer, the one or more booster compounds exhibits some affinitytowards the friction reducer.

In exemplary embodiments, the one or more iron-containing compounds andone or more booster compounds generates oligomeric fragments of theacrylamide-containing polymer. In exemplary embodiments, the oligomericfragments of the acrylamide-containing polymer generated by one or moreiron-containing compounds and one or more booster compounds arebiodegradable. In exemplary embodiments, the one or more iron-containingcompounds and one or more booster compounds generates oligomericfragments of the acrylamide-containing polymer having a molecular weightof less than about 400,000, about 300,000, or about 200,000 g/mol.

In exemplary embodiments, the viscosity of the well treatment fluid withthe one or more iron-containing compounds and one or more boostercompounds is less than the viscosity of well treatment fluid without theone or more iron-containing compounds and one or more booster compounds.

In exemplary embodiments, the decrease in the viscosity of the welltreatment fluid allows for easier recovery of the well treatment fluid.In exemplary embodiments, the viscosity of the well treatment fluid withthe one or more iron-containing compounds and one or more boostercompounds is less than the viscosity of well treatment fluid with theone or more iron-containing compounds but without the one or morebooster compounds.

In exemplary embodiments, the one or more iron-containing compounds andone or more booster compounds reduce the viscosity of the well treatmentfluid faster than conventional breakers. In exemplary embodiments, theone or more iron-containing compounds and one or more booster compoundsreduce the viscosity of the well treatment fluid faster than ammoniumpersulfate. In exemplary embodiments, the one or more iron-containingcompounds and one or more booster compounds acting on the well treatmentfluid increases the fracture conductivity within the formation.

In exemplary embodiments, the one or more iron-containing compounds andone or more booster compounds reduce the viscosity of the well treatmentfluid to less than about 10 cP at a shear rate of 10 s⁻¹, about 5 cP ata shear rate of 10 s⁻¹, about 2 cP at a shear rate of 10 s⁻¹, about 20cP at a shear rate of 100 s⁻¹, about 10 cP at a shear rate of 10 s⁻¹, orabout 3 cP at a shear rate of 10 s⁻¹.

Suitable adjustments to the ratios of the components that will affectthe conditions in which the viscosity of the well treatment fluid isreduced, or in which the acrylamide-containing polymer breaks down, willbe apparent to those of skill in the art.

In exemplary embodiments, the one or more iron-containing compounds andone or more booster compounds initiates breaking at ambienttemperatures. In exemplary embodiments, the one or more iron-containingcompounds and one or more booster compounds initiates breaking underheating.

In the exemplary embodiments, the well treatment fluid may be handled orprocessed in any manner as necessary or desired. In exemplaryembodiments, the well treatment fluid should be handled in compliancewith governmental regulations. In exemplary embodiments, the welltreatment fluid may be disposed of, processed for environmentalremediation, or recycled. In the exemplary embodiments, the one or moreiron-containing compounds and one or more booster compounds may be usedin the disposal, environmental remediation or recycling of the welltreatment fluid. In the exemplary embodiments, recycled well treatmentfluid may be used at any point where well treatment fluid is used.

EXAMPLES Example 1 Effect of Combinations of Exemplary Booster CompoundsIron-Containing Compounds and Commercially Available Breakers on theViscosity of Polyacrylamide Solutions

In this example, reduction in the viscosity of a well treatment fluidwas examined by treatment with exemplary iron-containing breakercompounds (Ferrous Sulfate, commercially available from FisherScientific) or commercially available (comparative) breakers (Ammoniumpersulfate (APS), commercially available from Fisher Scientific), withor without exemplary booster compounds (urea, EDTA, EDTA tetrasodium,all commercially available from Fisher Scientific).

Several polymer samples were prepared using a solution of 0.4 wt %partially hydrolyzed polyacrylamide (based on actives, available fromKemira Oyj). The samples were prepared by mixing the breaker and boostercompounds (as indicated) (either as a 1% solution in water or as apowder) with the partially hydrolyzed polyacrylamide solution. Theiron-containing breakers or the comparative breakers were added to thesamples to provide 0.01 wt % of breaker to the sample formulation. Whenincluded in a formulation, booster compounds were added to provide 0.01wt % booster to the sample formulation. One control sample (labeled“linear polymer” was prepared without breaker or booster compounds.

Each sample was heated at 150° F. for about 1 hour. The samples weresubsequently cooled to ambient temperature before analysis. Theviscosity of each sample was determined at 12 rpm at 72° F. in theBrookfield viscometer. The resulting viscosity of the samples isgraphically illustrated in FIG. 1.

In the preceding specification, various exemplary embodiments have beendescribed. It will, however, be evident that various modifications andchanges may be made thereto, and additional embodiments may beimplemented, without departing from the broader scope of the exemplaryembodiments as set forth in the claims that follow. The specificationand drawings are accordingly to be regarded in an illustrative ratherthan restrictive sense.

1. A method for fracturing a subterranean formation penetrated by a wellbore, the method comprising the step of injecting a well treatment fluidinto the well bore at a pressure and flow rate sufficient to fracturethe subterranean formation, wherein the well treatment fluid compriseswater, at least one acrylamide-containing polymer, one or moreiron-containing compounds and one or more booster compounds.
 2. A methodfor fracturing a subterranean formation penetrated by a well bore, themethod comprising the steps of (i) injecting a first well treatmentfluid comprising at least one acrylamide-containing polymer into thewell bore at a pressure and flow rate sufficient to fracture thesubterranean formation; and (ii) injecting a second well treatment fluidcomprising a one or more iron-containing compounds and one or morebooster compounds into the well bore.
 3. A method for fracturing asubterranean formation penetrated by a well bore, the method comprisingthe steps of (i) injecting a first well treatment fluid comprising atleast one acrylamide-containing polymer into the well bore at a pressureand flow rate sufficient to fracture the subterranean formation; (ii)injecting a second well treatment fluid comprising one or moreiron-containing compounds; and (iii) injecting a third well treatmentfluid comprising one or more booster compounds into the well bore. 4.The method of claim 2, wherein the first well treatment fluid furthercomprises a proppant.
 5. The method of claim 2, wherein the second welltreatment fluid further comprises a proppant.
 6. The method of claim 1,wherein the third well treatment fluid further comprises a proppant. 7.The method of claim 1, wherein the one or more iron-containing compoundscomprises a ferrous salt.
 8. The method of claim 1, wherein the one ormore iron-containing compounds is selected from the group consisting offerrous chloride, ferrous bromide, ferrous fluoride, ferrous sulfate,ammonium iron sulfate and combinations thereof.
 9. The method of claim1, wherein the one or more iron-containing compounds comprises ferrouschloride.
 10. The method of claim 1, wherein the one or moreiron-containing compounds comprises ferrous sulfate.
 11. The method ofclaim 1, wherein the one or more booster compounds are selected from thegroup consisting of urea; ethylenediaminetetraacetic acid (EDTA); saltsof EDTA; citric acid; aminotricarboxylic acid and its salts;polyphosphonated and poly phosphate compounds; boric acid and its salts;alkali metal salts of carbonates; diethylenetriaminepentaacetic acid(DTPA); humic acids; and lignosulfates.
 12. The method of claim 1,wherein the at least one acrylamide-containing polymer is selected fromthe group consisting of: acrylamide homopolymers, copolymers, andterpolymers; polyacrylamide; polyacrylamide derivatives; methacrylamidehomopolymers, copolymers, and terpolymers; diacetone acrylamidepolymers; N-methylolacrylamide polymers; and combinations thereof.
 13. Awell treatment fluid comprising water, one or more iron-containingcompounds and one or more booster compounds, and at least oneacrylamide-containing polymer.
 14. A method for reducing the viscosityof a well treatment fluid, the method comprising adding one or moreiron-containing compounds and one or more booster compounds to the welltreatment fluid, wherein the well treatment fluid comprises water and atleast one acrylamide-containing polymer.
 15. The method of claim 3,wherein the first well treatment fluid further comprises a proppant. 16.The method of claim 3, wherein the second well treatment fluid furthercomprises a proppant.
 17. The method of claim 2, wherein the one or moreiron-containing compounds comprises a ferrous salt.
 18. The method ofclaim 3, wherein the one or more iron-containing compounds comprises aferrous salt.
 19. The method of claim 2, wherein the one or more boostercompounds are selected from the group consisting of urea;ethylenediaminetetraacetic acid (EDTA); salts of EDTA; citric acid;aminotricarboxylic acid and its salts; polyphosphonated and polyphosphate compounds; boric acid and its salts; alkali metal salts ofcarbonates; diethylenetriaminepentaacetic acid (DTPA); humic acids; andlignosulfates.
 20. The method of claim 3, wherein the one or morebooster compounds are selected from the group consisting of urea;ethylenediaminetetraacetic acid (EDTA); salts of EDTA; citric acid;aminotricarboxylic acid and its salts; polyphosphonated and polyphosphate compounds; boric acid and its salts; alkali metal salts ofcarbonates; diethylenetriaminepentaacetic acid (DTPA); humic acids; andlignosulfates.